The present invention relates generally to methods and apparatus for perforating, and more specifically relates to methods and apparatus for retaining shaped charges in a perforating gun.
After an oil or gas well is drilled, casing is typically placed in the well to line the side of the wellbore. Before the well is placed on production, the casing and the producing formation are perforated. Ordinarily, perforating guns are lowered into the well until they are adjacent the formation to be produced. The guns are then detonated, perforating the casing and the formation, and the well may be produced.
Typically, the perforating gun includes a plurality of shaped charges mounted at spaced intervals in a charge carrier. The shaped charges are detonated by means of a detonating cord. Typically the charge carrier takes the form of a hollow cylindrical tube retained within a housing. The housing is adapted to be coupled to the tubing string or to a wireline. The charge carrier tube will include apertures, machined or stamped in the side of the carrier tube, to receive the shaped charges.
In the past, the shaped charges have been mounted in the charge carrier by means of various apparatus, including flat retention bands, threaded assemblies, and bolted flanges. Typically, these prior art apparatus have served to both retain the charges in place in the charge carrier and hold the detonating cord in contact with the shaped charges. As a result, when installing the shaped charges in the charge carrier, it has been necessary to simultaneously ensure that the detonating cord is properly aligned in the mounting clip with the shaped charge.
These conventional methods of mounting shaped charges has several disadvantages. First, the methods are very time consuming since such typical conventional mounting apparatus must be separately inserted into the charge holder before the shaped charge is installed. In addition, conventional mounting apparatus typically cannot satisfactorily be attached to either the shaped charges or the charge carrier prior to assembly of the shaped charge in the carrier. These conventional apparatus thus provide extra pieces to assemble at the well site, and may be easily lost or misplaced.
Accordingly, the present invention provides a securing method and apparatus whereby a shaped charge can be easily mounted in the charge holder and operatively secured to the detonating cord; and whereby the securing apparatus may be affixed to the shaped charges prior to mounting of the shaped charges in the perforating gun.